High definition LiDAR system

ABSTRACT

A LiDAR-based 3-D point cloud measuring system includes a base, a housing, a plurality of photon transmitters and photon detectors contained within the housing, a rotary motor that rotates the housing about the base, and a communication component that allows transmission of signals generated by the photon detectors to external components. In several versions of the invention, the system includes a vertically oriented motherboard, thin circuit boards such as ceramic hybrids for selectively mounting emitters and detectors, a conjoined D-shaped lens array, and preferred firing sequences.

PRIORITY CLAIM AND CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a reissue continuation of application Ser. No.15/180,580, filed Jun. 13, 2016, which is an application for reissue ofU.S. Pat. No. 8,767,190, issued Jul. 1, 2014, which claims the benefitof U.S. provisional application Ser. No. 61/345,505 filed May 17, 2010and which is a continuation-in-part of U.S. application Ser. No.11/777,802, now U.S. Pat. No. 7,969,558, filed Jul. 13, 2007, andfurther which claims the benefit of U.S. provisional application Ser.No. 60/807,305 filed Jul. 13, 2006, and U.S. provisional applicationSer. No. 61/345,505 filed May 17, 2010. Notice: more than one reissueapplication has been filed for the reissue of U.S. Pat. No. 8,767,190.The reissue applications include U.S. application Ser. No. 15/180,580,filed Jun. 13, 2016; U.S. application Ser. Nos. 15/700,543, 15/700,558,15/700,571, 15/700,836, 15/700,844, 15/700,959 (the presentapplication), and 15/700,965, each of which was filed on Sep. 11, 2017;and U.S. application Ser. No. 16/912,648, filed Jun. 25, 2020. Thecontents of each of the foregoing applications (other than U.S.application Ser. No. 16/912,648) are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention concerns the use of light pulses that aretransmitted, reflected from external objects, and received by a detectorto locate the objects in the field of view of the transmitter. Bypulsing a laser emitter and receiving the reflection, the time requiredfor the pulse of light to return to the detector can be measured,thereby allowing a calculation of the distance between the emitter andthe object from which the pulse was reflected.

When multiple pulses are emitted in rapid succession, and the directionof those emissions is varied, each distance measurement can beconsidered a pixel, and a collection of pixels emitted and captured inrapid succession (called a “point cloud”) can be rendered as an image oranalyzed for other reasons such as detecting obstacles. Viewers thatrender these point clouds can manipulate the view to give the appearanceof a 3-D image.

In co-pending application Ser. No. 11/777,802, the applicant described avariety of systems for use in creating such point cloud images usingLaser Imaging Detection and Ranging (LiDAR). In one version, the LiDARsystem was used for terrain mapping and obstacle detection, andincorporated as a sensor for an autonomous vehicle. An exemplary LiDARsystem included eight assemblies of eight lasers each as shown in FIG.1, or two assemblies of 32 lasers each forming a 64-element LiDAR systemas shown in FIG. 2. Yet other numbers of lasers or detectors arepossible, and in general the LiDAR was employed in an assemblyconfigured to rotate at a high rate of speed in order to capture a highnumber of reflected pulses in a full circle around the LiDAR sensor.

The preferred examples of the present invention described further belowbuild on the inventor's prior work as described above, incorporatingseveral improvements to reduce the overall size and weight of thesensor, provide better balance, reduce crosstalk and parallax, andprovide other advantages.

SUMMARY OF THE INVENTION

The present invention provides a LiDAR-based 3-D point cloud measuringsystem. An example system includes a base, a housing, a plurality ofphoton transmitters and photon detectors contained within the housing, arotary motor that rotates the housing about the base, and acommunication component that allows transmission of signals generated bythe photon detectors to external components.

In one version of the invention, the system provides 32 emitter/detectorpairs aligned along a vertical axis within a housing that spins toprovide a 360 degree field of view. The emitters may be aligned along afirst axis, with the detectors aligned along a second axis adjacent tothe first.

In a preferred implementation, the emitters and detectors are mounted onthin circuit boards such as ceramic hybrid boards allowing forinstallation on a vertical motherboard for a vertical configuration,improved alignment, and other advantages. The motherboard, in oneversion is formed with a hole in which the emitters fire rearward into amirror, reflecting the emitted light through the hole and through lensesadjacent the motherboard.

In certain configurations, the system employs a conjoint lens systemthat reduces or eliminates the parallax problem that may arise with theuse of separate emitter and detector optics.

In still further examples of the invention, the emitters fire in anon-adjacent pattern, and most preferably in a pattern in whichsequentially fired lasers are physically distant from one another inorder to reduce the likelihood of crosstalk.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings:

FIG. 1 is a front view of a rotating LiDAR system.

FIG. 2 is a perspective view of an alternate LiDAR system.

FIG. 3 is a perspective view of a preferred LiDAR system, showing anexemplary field of view of the laser emitters.

FIG. 4 is a side view of the preferred LiDAR system of FIG. 3.

FIG. 5 is a side view of the LiDAR system in accordance with FIG. 4,shown with the housing removed.

FIG. 6 is a perspective view of a hybrid containing a preferreddetector.

FIG. 7 is a perspective view of a hybrid containing a preferred emitter.

FIG. 8 is a back perspective view of the LiDAR system as shown in FIG.5.

FIG. 9 is a top perspective view of the LiDAR system as shown in FIG. 5.

FIG. 10 is an exemplary view of a LiDAR system with a potential parallaxproblem.

FIG. 11 is an exemplary front view of a lens assembly.

FIG. 12 is a sectional view of a lens assembly, taken along line A-A inFIG. 11.

FIG. 13 is a sectional view of an alternate lens assembly, taken alongline A-A in FIG. 11.

FIG. 14 is a representative view of a conjoined D-shaped lens solvingthe parallax problem of FIG. 10.

FIG. 15 is a front view of the LiDAR system as shown in FIG. 5.

FIG. 16 is an exemplary view of a rotary coupler for coupling a housingto a rotating head assembly.

FIG. 17 is an illustration of a potential crosstalk problem.

FIG. 18 is an illustration of a further potential crosstalk problem.

FIGS. 19A and 19B illustrate various circuits for driving laser diodes.

FIG. 20 illustrates example pulses generated for the laser diode.

FIGS. 21 and 22 illustrate results of operation of the circuit from FIG.19A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary LiDAR systems are shown in FIGS. 1 and 2. In each case, arotating housing fires light pulses that reflect from objects so thatthe return reflections may be detected by detectors within the rotatinghousing. By rotating the housing, the system provides a 360-degreehorizontal field of view (FOV) and, depending on the number andorientation of lasers within the housing, a desired vertical field ofview. The system is typically mounted on the top center of a vehicle,giving it a clear view in all directions, and rotates at a rate of about10 Hz (600 RPM), thereby providing a high point cloud refresh rate, suchhigh rate being advantageous for autonomous navigation at higher speeds.In other versions, the spin rate is within a range of about 5 to 20 Hz(300-1200 RPM). At this configuration, the system can collectapproximately 2.56 million time of flight (TOF) distance points persecond. The system therefore provides the unique combination of 360degree FOV, high point cloud density, and high refresh rate. Thestandard deviation of TOF distance measurements is equal to or less than2 cm. The LiDAR system may incorporate an inertial navigation system(INS) sensor system mounted on it to report x, y, z deviations andpitch, roll, and yaw of the unit that is used by navigational computersto correct for these deviations.

Through the use of DSP a dynamic power feature allows the system toincrease the intensity of the laser emitters if a clear terrainreflection is not obtained by photo detectors (whether due to reflectivesurface, weather, dust, distance, or other reasons), and to reduce powerto the laser emitters for laser life and safety reasons if a strongreflection signal is detected by photo detectors. A direct benefit ofthis feature is that the LiDAR system is capable of seeing through fog,dust, and heavy rain by increasing laser power dynamically and ignoringearly reflections. The unit also has the capability to receive anddecipher multiple returns from a single laser emission throughdigitization and analysis of the waveform generated by the detector asthe signal generated from the emitter returns.

The LiDAR systems of FIGS. 1 and 2 report data in the form of range andintensity information via Ethernet (or similar output) to a masternavigational system. Using standard trigonometry, the range data isconverted into x and y coordinates and a height value. The height valuecan be corrected for the vehicle's pitch and roll so the resulting mapis with reference to the horizontal plane of the vehicle. The map isthen “moved” in concert with the vehicle's forward or turning motion.Thus, the sensor's input is cumulative and forms an ultra-high-densityprofile map of the surrounding environment.

This highly detailed terrain map is then used to calculate obstacleavoidance vectors if required and to determine the maximum allowablespeed given the terrain ahead. The LiDAR system identifies of size anddistance of objects in view, including the vertical position and contourof a road surface. The anticipated offset of the vehicle from astraight, level path, either vertical or horizontal, at differentdistances is translated into the G-force that the vehicle will besubject to when following the proposed path at the current speed. Thatinformation can be used to determine the maximum speed that the vehicleshould be traveling, and acceleration or braking commands are issuedaccordingly. In all cases the software seeks the best available roadsurface (and thus the best possible speed) still within the boundariesof a global positioning system (GPS) waypoint being traversed.

One version of the inventor's prior system as illustrated in FIG. 1includes 64 emitter/detector (i.e. laser diode/photo diode) pairsdivided into eight groups of eight. The system shown in FIG. 2 alsoincludes 64 emitter/detector pairs, but in a configuration of 2assemblies of 32 pairs. It is also possible to “share” a single detectoramong several lasers by focusing several detection regions onto a singledetector, or by using a single, large detector. By firing a single laserat a time, there would be no ambiguity as to which laser is responsiblefor a return signal. Conversely, one could also sub-divide a singlelaser beam into several smaller beams. Each beam would be focused ontoits own detector. In any event, such systems are still consideredemitter-detector pairs.

In the versions as illustrated in FIGS. 1 and 2, the laser diode ispreferably an OSRAM 905 nm emitter, and the photo diode is preferably anAvalanche variety. More particularly, in the preferred version each oneof the detectors is an avalanche photodiode detector. The lenses arepreferably UV treated to block sunlight, or employ a separate UV lensfilter in the optical path. Each pair is preferably physically alignedin ⅓° increments, ranging from approximately 2° above horizontal toapproximately 24° below horizontal. Each of the emitter/detector pairsare controlled by one or more DSPs (or, in some versions, fieldprogrammable gate arrays, or FPGAs, or other microprocessor), whichdetermines when they will fire, determines the intensity of the firingbased on the previous return, records the time-of-flight, calculatesheight data based time-of-flight and angular alignment of each pair.Results, including multiple returns if any, are transmitted via Ethernetto the master navigational computer via a rotary coupling.

It is also advantageous to fire only several lasers, or preferably justone, at a time. This is because of naturally occurring crosstalk, orsystem blinding that occurs when the laser beam encounters aretroreflector. Such retroreflectors are commonly used along theroadways. A single beam at a time system is thus resistant toretroreflector blinding, while a flash system could suffer severe imagedegradation as a result.

In addition to crosstalk concerns, firing single lasers at once whilerotating at a high rate facilitates eye safety. The high powered lasersused with the present preferred versions of the invention would requireprotective eyewear if the system was used in a stationary fashion.Rotation of the system and firing fewer lasers at once for brief pulsesallows high powered lasers to be used while still meeting eye safetyrequirements that do not require protective eyewear. In accordance withthis aspect of the invention, the system employs a control componentthat does not allow the emitters to fire until the head has reached adesired minimal rotation speed.

Another advantage of firing only a small number of lasers at a time isthe ability to share, or multiplex, the detection circuitry amongseveral detectors. Since the detection circuitry consists of high speedAnalog to Digital Converters (ADCs), such as those made by NationalSemiconductor, considerable cost savings can be had by minimizing theuse of these expensive components.

In the preferred embodiment, the detectors are power cycled, such thatonly the desired detector is powered up at any one time. Then thesignals can simply be multiplexed together. An additional benefit ofpower-cycling the detectors is that total system power consumption isreduced, and the detectors therefore run cooler and are therefore moresensitive.

A simple DC motor controller driving a high reliability brushed orbrushless motor controls the rotation of the emitter/detectors. A rotaryencoder feeds rotational position to the DSPs (or other microprocessor)that use the position data to determine firing sequence. Software andphysical fail-safes ensure that no firing takes place until the systemis rotating at a minimum RPM.

FIG. 2 illustrates a perspective view of a 64 emitter/detector pairLiDAR component 150. The component 150 includes a housing 152 that isopened on one side for receiving a first LiDAR system 154 located abovea second LiDAR system 156. The second LiDAR system 156 is positioned tohave line of sight with a greater angle relative to horizontal than thefirst LiDAR system 154. The housing 152 is mounted over a base housingsection 158.

The LiDAR system of FIG. 2 includes a magnetic rotor and stator. Arotary coupling, such as a three-conductor Mercotac model 305, passesthrough the center of the base 158 and the rotor. The three conductorsfacilitated by the rotary coupling are power, signal, and ground. Abearing mounts on the rotary coupling. A rotary encoder has one partmounted on the rotary coupling and another part mounted on the basesection 158 of the housing 152. The rotary encoder, such as a U.S.Digital Model number E65-1000-750-I-PKG1 provides information regardingto rotary position of the housing 152. The magnetic rotor and statorcause rotary motion of the base section 158 and thus the housing 152about the rotary coupling.

The version described below with reference to FIGS. 3-16 is generallyreferred to as an High Definition LiDAR 32E (HDL-32E) and operates onthe same foundational principles as the sensors of FIGS. 1 and 2 in thata plurality (in this embodiment up to 32) of laser emitter/detectorpairs are aligned along a vertical axis with the entire head spinning toprovide a 360 degrees horizontal field of view (FOV). Each laser issueslight pulses (in this version, 5 ns pulses) that are analyzed fortime-of-flight distance information (called a “distance pixel” or“return”). Like the system of FIG. 2, the system reports returns inEthernet packets, providing both distance and intensity (i.e. therelative amount of light received back from the emitter) information foreach return. The sample system reports approximately 700,000 points persecond. While all or any subset of the features described above withrespect to FIGS. 1 and 2 may be incorporated into the version describedbelow with respect to FIGS. 3-16, alternate embodiments of the inventionmay optionally include the additional aspects as described in detailbelow.

In a preferred version as illustrated in FIG. 3, the cylindrical sensorhead 10 is about 3.5 inches in diameter and the unit has an overallheight of 5.6 inches and weighs about 2.4 pounds. By contrast, theHDL-64E (shown in FIG. 2) is 8 inches in diameter by approximately onefoot tall, and weighs about 29 pounds. This reduction in size is theresult of several inventive improvements, as described more fully below.

The sample embodiment of FIG. 3 can be built with a variable number oflasers, aligned over a vertical FOV 12 of +10 to −30 degrees as bestseen in FIG. 4. The vertical FOV may be made larger or smaller, asdesired, by adjusting the number or orientation of the emitters anddetectors. When using the emitters as described and orienting them asdescribed, the range is approximately 100 meters. The head 10 is mountedon a fixed platform 14 having a motor configured such that it preferablyspins at a rate of 5 Hz to 20 Hz (300-1200 RPM). The sample system uses905 nm laser diodes (although other frequencies such as 1550 nm could beused) and is Class 1 eye safe.

FIG. 5 illustrates the same version as shown in FIGS. 3 and 4, thoughwithout the outer housing covering the internal components. In general,and as discussed more fully below, the system includes a mainmotherboard 20 supporting a plurality of detector hybrids 32 and emitterhybrids (not visible in FIG. 5). The emitters fire back toward the rearof the system, where the pulses are reflected from a mirror and then aredirected through a lens 50. Return pulses pass through a lens, arereflected by a mirror 40, then directed to the detectors incorporatedinto the hybrids 32. The motherboard 20 and mirror 40 are mounted to acommon frame 22 providing common support and facilitating alignment.

The hybrids 32 are mounted to the motherboard in a fan pattern that isorganized about a central axis. In the version as shown, 32 hybrids areused in a pattern to create a field of view extending 10 degrees aboveand 30 degrees below the horizon and therefore the central axis extendsabove and below the ninth board 38, with 8 boards above and 23 boardsbelow the central axis. In one version, each successive board isinclined an additional one and one-third degree with respect to the nextadjacent board. The desired incremental and overall inclination may bevaried depending on the number of hybrids used, the geometry of themirrors and lenses, and the desired range of the system.

One of the features allowing for compact size and improved performanceof the version of FIG. 3 is the use of thin circuit boards such asceramic hybrid boards for each of the emitters and detectors. Anexemplary detector circuit board 32 is shown in FIG. 6; an exemplaryemitter circuit board 30 is shown in FIG. 7. In the preferred example,the thin circuit boards are in the form of ceramic hybrid boards thatare about 0.015 inches thick, with only one emitter mounted on eachemitter board, and only one detector mounted on each detector board. Inother versions the thin circuit boards may be formed from othermaterials or structures instead of being configured as ceramic hybrids.

One of the advantages of mounting emitters and detectors on individualhybrid boards is the ability to then secure the individual hybrid boardsto the motherboard in a vertically aligned configuration. In theillustrated version, the detectors are positioned in a first verticalalignment along a first vertical axis while the emitters are positionedin a second vertical alignment along a second vertical axis, with thefirst and second vertical axes being parallel and next to one another.Thus, as best seen in FIGS. 5 and 8, the hybrid boards carrying theemitters and detectors are mounted in vertical stacks that allow thesensor head to have a smaller diameter than a differently configuredsensor having emitters and detectors positioned about the circumferenceof the system. Accordingly, the configuration reduces the overall sizeand requires less energy for spinning by moving more of the weighttoward the center of the sensor.

As further shown in FIG. 8, the preferred version incorporates aplurality of detectors (in this case, 32 of them) mounted to an equalnumber of detector hybrids 32. The system likewise has the same numberof emitters mounted to an equal number of emitter hybrids 30. In thepreferred version, the system therefore has one emitter per hybrid andone detector per hybrid. In other versions this may be varied, forexample to incorporate multiple emitters or detectors on a singlehybrid. The emitter and detector hybrids are connected to a commonmotherboard 20, which is supported by a frame 22. The motherboard has acentral opening 24 that is positioned to allow emitted and receivedpulses to pass through the motherboard. Because the lenses arepositioned over the middle of the motherboard, the central opening isconfigured to be adjacent the lenses to allow light to pass through theportion of the motherboard that is next to the lenses.

The density of emitter/detector pairs populated along the vertical FOVis intentionally variable. While 32 pairs of emitters and detectors areshown in the illustrated versions, the use of hybrids and a motherboardallows for a reduction in the number of emitters and detectors by simplyremoving or not installing any desired number of emitter/detector pairs.This variation of the invention cuts down on the number vertical linesthe sensor produces, and thus reduce cost. It is feasible that just afew emitter/detector pairs will accomplish the goals of certainautonomous vehicles or mapping applications. For some uses increaseddensity is desirable to facilitate seeing objects at further distancesand with more vertical resolution. Other uses exploit the fact thatthere is a direct relationship between the number of emitter detectorpairs and sensor cost, and do not need the full spread of verticallasers to accomplish their sensor goals.

Alternatively, multiple emitters and detectors can be designed andmounted onto the hybrid boards at slightly different vertical angles,thus increasing the density of vertical FOV coverage in the samefootprint. If, for example, two emitters and two detectors were mountedon each of the hybrids shown in FIGS. 6 and 7 with slight verticaloffsets, the design would incorporate 64 emitters and detectors ratherthan 32. This example design describes two emitters and detectorsmounted per board, but there is no practical limit to the number ofemitters and detectors that may be mounted on a single board. Theincreased number of emitters and detectors may be used to increase thefield of view by adjusting the relative orientation, or may be used toincrease the density of points obtained within the same field of view.

Another design feature of the preferred version is the verticalmotherboard on which the main electronics that control the firing of thelasers and the capturing of returns are located. As noted above, themotherboard is mounted vertically, defining a plane that is preferablyparallel to the central axis 13 (see FIG. 3) about which the system willrotate. While the motherboard is preferably parallel to this axis ofrotation, it may be inclined toward a horizontal plane by as much as 30degrees and still be considered substantially vertical in orientation.The emitter and detector hybrid boards are aligned and soldered directlyto this vertical motherboard, thus providing for small overall head sizeand increased reliability due to the omission of connectors that connectthe laser boards with the motherboard. This board is mechanicallyself-supported, mounted to a frame 22 that fixes it rigidly in positionin a vertical orientation so that it spins with the rotating sensorhead. The insertion of the hybrid boards can be automated for easyassembly. Prior art sensors exclusively employ motherboard designrequiring connectors and cables between the emitters and detectors andthe motherboard. The positioning and configuration of the motherboard asshown overcomes these problems.

Another feature of the vertical motherboard design is its proximityinside the sensor head. In order to optimize space, the motherboard ispositioned between the mirror and the lenses, as best seen in FIG. 9.Thus, as shown, the sensor head includes one or more lenses 50, 52supported within a lens frame 54 positioned at a front side of thesensor head. One or more mirrors 40, 42 are positioned at the oppositeside of the sensor head and mounted to the frame 22. In the illustratedversion, separate mirrors 40, 42 are used for the emitter and detectors,respectively. Most preferably, the frame 22 is a unitary frame formedfrom a single piece of material that supports the motherboard and themirrors.

This configuration allows the hybrid emitters to fire rearward into thefirst mirror 40, wherein the light then reflects off the mirror andtravels through the hole 24 in the motherboard 20, through the lens 50and so that the emitted light 60 travels out to the target 70. Thisconfiguration further increases the net focal length of the light pathwhile retaining small size. Likewise the returning light 62 passesthrough the detector lens 52, through the hole 24 in the motherboard tothe opposite mirror 52 and is reflected into the corresponding detector.

Another benefit of the vertical motherboard design is that itfacilitates the goal of balancing the sensor head both statically anddynamically to avoid shimmy and vibration during operation. Mostpreferably, the various components are positioned to allow anear-balanced condition upon initial assembly that requires a minimum offinal static and dynamic balancing counterweights. As best seen in FIG.9, this balancing is obtained by positioning major portions ofcomponents about the circumference of the sensor head. Morespecifically, the lenses and frame are on one side while the mirrors anda generally T-shaped portion of the frame is diametrically opposite thelenses, with the mirrors and rearward portion of the frame configured tohave a weight that is about equal to that of the lenses and lens frame.Likewise, the emitter and detector hybrids are carried on diametricallyopposite sides of the sensor head, positioned at about a 90 degreeoffset with respect to the lens and mirror diameter. The motherboard isnearly along a diameter, positioned to counter balance the weight of theother components, such that the center of gravity is at the center ofrotation defined by the center of the base 80.

When the present invention is incorporated into an autonomous navigationor mobile mapping vehicle, GPS and inertial sensors are often includedto locate the vehicle in space and correct for normal vehicle motion.Inertial sensors often include gyros, such as fiber optic gyros (FOG),and accelerometers. In one embodiment, there is a 6-axis inertial sensorsystem mounted in the LiDAR base and the signals from the gyros andaccelerometers are output along with the LiDAR distance and intensitydata.

The separate location of emitters' and detectors' optical paths cancreate a parallax problem. When the emitters and detectors are separatedby a finite distance there always exists a “blind” region nearest to thesensor in which objects cannot be illuminated or detected. Likewise, atlong range the emitter's laser light becomes misaligned with itscorresponding detector and creates a similar blind spot. The parallaxproblem is best seen with reference to FIG. 10. A representative emitter170 transmits a light signal through a lens 172, with the propagatedlight signal traveling outward and toward a target in the distance.Light reflected from a target may return through a second lens 162 andonward toward a detector 160. The nonparallel orientation of the emitterand detector, however, creates nonparallel light emitter and detectorpaths. Consequently, there is a near blind spot 180 adjacent the systemand a far blind spot 184 more distant from the system. In either of thetwo blind spots, light reflecting from an object will return along apath that cannot be received by the detector. The near blind spotextends for a distance “A” in front of the system, while the far blindspot extends in the region of distance “C” beyond the system. Betweenthe two blind spots, in a distance defined by “B”, the system will seean object in that light reflected from the object can return along apath that can be detected. Even within region B, however, there is a“sweet spot” 182 defined by the straight line paths of travel from theemitter and to the detector. For the sample embodiment shown in FIGS. 1and 2 the “sweet spot” 182 for parallax alignment is approximately 100feet from the centerline of the sensor. Inside of about 10 feet theemitter's light misses its corresponding detector entirely, shown at180, and beyond approximately 240 feet, shown at 184, the signal becomesweak due to the misalignment of the emitter and detector in the oppositedirection.

This effect can be alleviated in one version of the invention by havingtwo “D”-shaped lenses 50, 52 (see FIG. 15), constructed for the emitterand detector, and having these two lenses attached to each other with aminimal gap in between. The close proximity of the conjoint lens system,best seen in FIG. 14, reduces the “blind” region to near zero, as shownby the parallel nature of the emitter's light 60 and detector's lightpath 62.

Due to the complex nature of the optical propagation in lenses, a lensarray is usually needed to correct for various aberrations that arecommonly associated with any optical design. For the purpose ofconstructing a conjoint lens system to overcome the parallax problemdescribed with respect to FIG. 10, it is useful to have the firstsurface of the lens array being the largest pupil; that is, the opticalrays entering the lens system should bend towards the center.

FIG. 11 illustrates a front view of a lens array 50. Though indicated asthe emitter lens array, it may also be illustrative of the detector lensarray as well. In order to form a D-shaped lens, an edge 51 of theotherwise circular lens is cut away from the lens, removing a left edge120 of the otherwise circular lens. The resulting lens is somewhatD-shaped, having a vertical left edge. The use of a D-shaped lens arrayis advantageous in that D-shaped lens arrays for the emitter anddetector may be placed back-to-back to form “conjoined” D-shape lensarrays as best seen in FIG. 15. Placing the vertical edges of theD-shapes adjacent one another allows the otherwise circular lenses to bemuch closer to one another than would be the case if using circularlenses which would only allow for tangential contact between the lensarrays.

The creation of D-shaped lenses and the use of a conjoined pair ofD-shaped lens arrays, however, brings a potential signal loss. FIG. 12illustrates a correct design of the lens array, shown in sectional viewtaken along lines A-A from FIG. 11. In this illustration the lens arrayincludes a first lens 113, a second lens 111, and a third lens 112. Theinput rays 100 always bend towards the center in this lens array.Consequently, when a D-shaped cut is made (that is, cutting off aportion of one side of each of the lenses in the area indicated by theshaded region 120), there is no loss of light. As the shaded regionindicates, all of the light entering the first lens 113 travels throughthe entire lens array to the mirror.

FIG. 13 illustrates an incorrect design having a similar array of threelenses 110, 111, 112. In this case, the front lens 110 is differentlyshaped and some of the input light rays 100 bend away from the center asthey travel through the front lens. A cut through the ends of one sideof this lens array would result in the loss of some of the lightentering the array, as indicated in the shaded region 120 in FIG. 12.

By configuring the lenses in an ideal fashion as illustrated in FIG. 12,a portion of each side of the lens array may be cut in the form of aD-shape. This creates a straight edge along the sides of each lens inthe array, allowing the straight sides of the D's forming each lensarray to be positioned closely adjacent one another. In this sense, theterm “closely adjacent” is understood to mean either in contact with oneanother or positioned such that the center of the lenses are closer toone another than they could be without the D-shaped cut. As best see inFIG. 15, the two lens arrays 50, 52 are positioned closely adjacent oneanother with the straight sides back-to-back to form conjoined D-shapedlens arrays. As described above, a first lens array 50 serves as theemitter lens array while the adjacent second lens array 52 serves as thedetector lens array.

FIG. 14 illustrates an advantage of the conjoint D-shaped lens design,particularly in how it overcomes the parallax problem illustrated inFIG. 10. In this case, light emerging from the emitter 170 is directedto a first D-shaped lens 50. Most preferably, the emitter is oriented todirect its light path toward a position just inward of the straight sideedge of the D-shape. Because of the lens array configuration of the typedescribed in FIG. 12, the light emerges from the first lens 50 in astraight line 60 that can be directed radially away from the sensorhead. Likewise, light reflected from the distant object will returnalong a return path 62 that is parallel to the emitter light path. Theclosely parallel return path will travel through the second, adjacentconjoined D lens array 52, entering the lens array at a position justinward of the straight side edge of the D-shape, where it is thendirected to the detector 160. Consequently, there is no blind spot aswith conventional lenses and the parallax problem is resolved.

Another unique design consideration for the preferred implementationaddresses the need to transfer power and signal up to the head, andreceive signal and offer grounding down from the head. Off the shelfmercury-based rotary couplers are too unreliable and too big for thisproblem. In one embodiment, shown in FIG. 16, the use of a rotarytransformer 145 enables sending power up to the head, and the use of acapacitive coupler 140 down from the head to accommodate theserequirements. A phase modulation scheme allows for communication to thehead from the base using serial commands in order to instruct the headto limit horizontal field of view, fire all lasers at full power, updateits firmware, and other commands.

It is also desired to have the distance returns of the LiDAR scanner beas accurate as possible and be free of spurious images or returns.Firing multiple lasers at once can create a crosstalk condition wherethe light emitted from one laser inadvertently is detected by thedetector of another laser, thus giving a false return. Thus, withreference to FIG. 17, if emitters E1 through E4 all fire at once, theirreturns would be intended to be received by emitters D1 through D4. Butdepending on the positioning and configuration of the object from whichthe light returns, light from one of the emitters may be directed to thewrong detector. For example, as indicated in FIG. 17, light from emitterE1 may end up directed to detector D3, as indicated by the dotted linereturn path. This would be an invalid return, and the system woulderroneously associate it with light sent from emitter E3, therebycreating a faulty pixel in the point cloud.

A similar error can occur if adjacent lasers are fired in a sequentialfashion. Thus, with reference to FIG. 16, firing a single emitter E1 mayresult in light being detected at detector D2 rather than D1. This maymost commonly occur when light from emitter E1 travels beyond the truerange of the sensor but is reflected from a particularly reflectiveobject, such as a stop sign covered with reflective paint. The firing ofadjacent emitters in order makes this form of cross-talk more likely.

In accordance with a preferred version of the invention, the emittersare fired in a non-adjacent single laser firing order. This means thatonly one emitter detector pair is active at any given time, and at notime do adjacent emitters and detectors fire in sequence. Mostpreferably there is as much distance as possible between the emittersthat are fired in order. Thus, if there are 32 emitters in a verticalstack, the emitters would be assigned labels E1 representing thetop-most emitter and then sequentially numbered through E32 representingthe bottom emitter in the stack. Emitter E1 (at the top) would be firedfirst, followed by emitter E17 (in the middle of the stack), then E2,E18, E3, E19, and so on, ending with E16 and E32 before starting overagain at the beginning This pattern begins with the top emitter and themiddle emitter, dividing the stack into two groups. It then alternatesfiring one from each group, moving from the top of each half-stack andproceeding sequentially down each half-stack of emitters in an thisalternating fashion and then repeating. This pattern ensures the largestpossible distance between fired lasers, thereby reducing the chance ofcrosstalk.

FIGS. 19A and 19B illustrate circuits used for controlling the firing ofa laser diode. With regard to FIGS. 19A and 20, the DSP sends acharge/on signal to a FET 200, thereby charging an inductor 204, whichin turn charges a capacitor 206, which in turn causes a laser 210 tofire. The DSP turns off the FET 200 after a predetermined period of timeas previously determined by return intensity measurements from the lastpulse. The charging pulse is on for ˜5 microseconds and the firing pulseis on for ˜20 nanoseconds. It can be seen that the energy stored in theinductor is ½*L*I{circumflex over ( )}2. When the FET is turned off,this energy is transferred into the discharge capacitor via a diode. Theenergy in the capacitor is ½*C*V{circumflex over ( )}2. It is apparentthen that the voltage that is in the capacitor is proportional to the onduration of the FET. Therefore, the DSP can use a simple algorithm topredict the proper amount of voltage in the capacitor. For example, ifthe return pulse is ½ as large as desirable, from a noise andmeasurement accuracy point of view, then the DSP simply charges theinductor for twice as long for the next pulse. Of course, such a systemcannot see into the future, so it is not always possible to get theperfect return intensity every time. Nevertheless, the technique workswell enough most of the time for the system to benefit from technique.

FIG. 19B includes two FETs. When FET1 is on during a charging pulse(FIG. 20), an inductor 240 charges a capacitor 242. When the FET2 is onduring the firing pulse (see FIG. 20), FET2 causes the capacitor 242 todischarge thereby firing a laser diode 244.

FIG. 21 illustrates current and luminance output of the circuits ofFIGS. 19A and 19B. FIG. 22 shows digitized sensed values at the photodiode of the receiving side.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment. Instead, the invention should be determined entirely byreference to the claims that follow.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A LiDAR-based sensorsystem comprising: a base; head assembly; a rotary component configuredto rotate the head assembly with respect to the base, the rotation ofthe head assembly defining an axis of rotation; an electricalmotherboard carried in the head assembly, the motherboard defining aplane and being positioned substantially parallel to the axis ofrotation; a lens positioned on the head assembly on a first side of themotherboard; a mirror positioned on the head assembly on a second sideof the motherboard; a plurality of photon transmitters mounted to aplurality of emitter circuit boards, the plurality of emitter circuitboards being mounted directly to the motherboard; and a plurality ofdetectors mounted to a plurality of detector circuit boards, theplurality of detector circuit boards being mounted directly to themotherboard.
 2. The sensor system of claim 1, wherein the lens comprisesan emitter lens and a detector lens, the emitter lens and the detectorlens being positioned adjacent one another; and the mirror comprises anemitter mirror and a detector mirror; wherein the emitter mirror ispositioned within the head assembly to reflect light from the pluralityof photon transmitters through the emitter lens, and the detector mirroris positioned within the head to reflect light received through thedetector lens toward the plurality of detectors.
 3. The sensor system ofclaim 2, further comprising a unitary support structure, themotherboard, detector lens, emitter lens, detector mirror, and emittermirror all being secured to the unitary support structure.
 4. The sensorsystem of claim 2, wherein the plurality of emitters are oriented totransmit light from the second side of the motherboard toward theemitter mirror.
 5. The sensor system of claim 4, wherein the motherboardcomprises a central opening, the central opening being positioned toallow light from the emitters to pass from emitter mirror through thecentral opening and toward the emitter lens.
 6. The sensor system ofclaim 5, wherein the central opening is further positioned to allowlight to pass from the detector lens through the central opening andtoward the detector mirror.
 7. The sensor system of claim 2, wherein theplurality of emitter circuit boards are secured to the motherboard toform a first vertical stack.
 8. The sensor system of claim 7, whereinthe first vertical stack of emitter circuit boards forms an angularlyfanned array.
 9. The sensor system of claim 7, wherein the plurality ofdetector circuit boards are secured to the motherboard to form a secondvertical stack, the first vertical stack of emitter circuit boards beingpositioned substantially parallel to the second vertical stack ofdetector circuit boards.
 10. The sensor system of claim 9, wherein thesecond vertical stack of detector circuit boards forms an angularlyfanned array.
 11. The sensor system of claim 2, wherein the emitter lenscomprises a first D-shaped lens and the detector lens comprises a secondD-shaped lens, a respective vertical side of each of the first D-shapedlens and the second D-shaped lens being positioned closely adjacent oneanother to form a conjoined D-shaped lens array.
 12. The sensor systemof claim 11, wherein the first D-shaped lens comprises a first pluralityof lenses, and wherein the second D-shaped lens comprises a secondplurality of lenses.
 13. The sensor system of claim 2, wherein theplurality of emitter circuit boards are secured to the motherboard toform a first vertical stack, the first vertical stack being divided intoat least two groups of emitters, each of the at least two groupscomprising several emitters from the plurality of emitters such that theat least two groups form non-overlapping subsets of the plurality ofemitters, the sensor further having a control component to control thefiring of the emitters such that one emitter is fired at a time, thecontrol component further causing firing from one of the at least twogroups and then the other of the at least two groups in an alternatingfashion.
 14. The sensor system of claim 13, wherein the at least twogroups comprises: a first group forming a first portion of the firstvertical stack and organized sequentially from a first top position to afirst bottom position; and a second group forming a remaining portion ofthe first vertical stack organized sequentially from a second topposition to a second bottom position; whereby the control componentcauses firing of the emitters to alternate between the first group andthe second group, and further causes firing within the first group toproceed sequentially and firing within the second group to proceedsequentially.
 15. The sensor system of claim 2, wherein the rotarycomponent further comprises a capacitive coupler.
 16. A LiDAR-basedsensor system comprising: a base; head assembly; a motor configured torotate the head assembly with respect to the base, the rotation of thehead assembly defining an axis of rotation; an electrical motherboardcarried in the head assembly; a plurality of photon transmitters mountedto a plurality of emitter circuit boards, the plurality of emittercircuit boards being mounted to the motherboard; a plurality ofdetectors mounted to a plurality of detector circuit boards, theplurality of detector circuit boards being mounted to the motherboard;an emitter mirror supported within the head assembly; a detector mirrorsupported within the head assembly; and a conjoined D-shaped lensassembly, the lens assembly forming an emitter portion and a detectorportion; wherein the motherboard is a unitary component for mounting theplurality of emitter circuit boards and the plurality of detectorcircuit boards, the motherboard being positioned between the emittermirror and the detector mirror on a first side and the lens assembly onthe other side, the motherboard further having an opening to allow lightto pass between the lens assembly and either the detector mirror or theemitter mirror; whereby light transmitted by one of the plurality ofemitters is reflected from the emitter mirror and passes through theemitter portion of the lens assembly, and light received by the detectorportion of the lens assembly is reflected by the detector mirror andreceived by one of the plurality of detectors.
 17. The sensor system ofclaim 16, wherein the motherboard defines a plane that is parallel tothe axis of rotation.
 18. The sensor system of claim 17, furthercomprising: a control component for causing the firing of the pluralityof emitters; and further wherein there are n emitters in the pluralityof emitters, the n emitters being positioned in a vertical stack from 1to n, the plurality of emitters being divided into two groups, includinga first group of emitters from 1 to n/2 and a second group of emittersfrom n/2+1 to n; wherein the control component causes the emitters tofire alternatingly between the first group and the second group, and tofire sequentially within each group such that emitter 1 and emittern/2°1 fire sequentially.
 19. A LiDAR-based sensor system comprising: abase having a head assembly and a rotary component configured to rotatethe head assembly with respect to the base; a motherboard in the headassembly; a mirror at a periphery of the head assembly; a lens at theperiphery of the head assembly; a plurality of transmitters carried onthe head assembly for rotation with the head assembly, the plurality oftransmitters being positioned to transmit light pulses through the lens;a plurality of detectors carried on the head assembly for rotation withthe head assembly, the plurality of detectors being positioned toreceive the light pulses after reflection from a surface; a processorcoupled to a control circuit; and a memory including processorexecutable code, wherein the processor executable code, upon executionby the processor, configures the processor to send one or more signalsto control the control circuit to cause one of the transmitters to fire.20. The sensor system of claim 19, wherein the control circuit includesa transistor, an inductor, and a capacitor, and wherein sending the oneor more signals to control the control circuit to cause one of thetransmitters to fire comprises: sending a charge/on signal to thetransistor to charge the inductor; and turning off the charge/on signalto transfer energy from the inductor into the capacitor, which causesthe one transmitter to fire.
 21. The sensor system of claim 20, whereinthe charge/on signal is turned off after a period of time that isinversely proportional to the return intensity of the previous lightpulse transmitted by the one transmitter.
 22. The sensor system of claim19, wherein the control circuit includes a first transistor, a secondtransistor, an inductor, and a capacitor, and wherein sending the one ormore signals to control the control circuit to cause one of thetransmitters to fire comprises: sending a charge/on signal to the firsttransistor to cause the inductor to charge the capacitor; and sending afiring pulse to the second transistor to cause the capacitor todischarge and fire the one transmitter.
 23. The sensor system of claim19, wherein sending the one or more signals to control the controlcircuit to cause one of the transmitters to fire comprises: sending theone or more signals to control charging and discharging of a chargestorage device of the control circuit, wherein the discharging of thecharge storage device causes the one transmitters to fire.
 24. A methodcomprising: rotating a head assembly of a LiDAR-based sensor system withrespect to a base of the LiDAR-based sensor system, the LiDAR-basedsensor system having a plurality of transmitters positioned to transmitlight pulses and a plurality of detectors positioned to receive thelight pulses after reflection from a surface, the plurality oftransmitters being mounted to a respective plurality of transmittercircuit boards, the plurality of detectors being mounted to a respectiveplurality of receiver circuit boards, the pluralities of transmittercircuit boards and detector circuit boards being mounted to amotherboard of the LiDAR-based sensor system; and controlling chargingand discharging of a plurality of charge storage devices correspondingto the plurality of transmitters, wherein the discharging of the chargestorage devices causes the respective transmitters to fire.